Arrangement for controlling processes

ABSTRACT

A control arrangement for processes involving a plurality of control variables and an output variable depending in a complex manner on the various control variables wherein the deviation between the output vectors of a reference model and of the process is employed and on the basis of this deviation the synthesis of the control vector is formed so that the output variables of the process will follow the output variables of the reference model without it being necessary to know the relationships between the input variables and the output variables.

United States Patent Courtiol Mar. 5, 1974 ARRANGEMENT FOR CONTROLLING [73] Assignee: Societe Generale De Constructions Electriques Et Mechniques (Alsthom Paris, France Filed: July 5, 1972 Appl. No.: 269,144

Foreign Application Priority Data Primary Examiner-Eugene G. Bo'tz Attorney, Agent, or Firm'Craig and Antonelli [57] ABSTRACT A control arrangement for processes involving a plurality of control variables and an output variable depending in a complex manner on the various control variables wherein the deviation between the output [30] vectors of a reference model and of the process is em- July 5, France ployed and on the of deviation the ynthesis of the control vector is formed so that the output vari- US. Clv .t ables of the process output ariables of [5 l 1 Cl. u the reference model without being necessary to Fleld. 0 Search 1 1 l 2 know the relationships between the input variables and the output variables. [56] References Cited UNITED STATES PATENTS 10 Claims, 21 Drawing Figures 3,446,946 5/1969 Andeen 235/l50.l

COMPUTER l O 5 a l LINEAR l comma e I (P) 1 I REFERENCE 2 1 2 MODEL' K C V l WP) r l 1 NW E! mm PORTION l l =13 i PATENTED 5W 3.795.799

sum 010F17 FIG! 3 6P COMPARATOR GENERALIZED DEVIATION MATRICES PROCEss1 P(p) 5- Kp 6\ Ke PROCESS RETURN MATRICES ZREFERENCE MODEL ADDERB ADDER7 PROCESS INPUT 4 Ku MATRICES PATENTED 51974 FIG.2

REFERENCE PROCESS mm MATRICES PATENIEI] MAR 5 I974 saw "on or 17 FIGS (FIG. 4)

(FIG. 4)

Cm(u) (-FIG.4)

(FIG. 4)

22 (FIG 4) (FIG. 4)

(FIG. 4)

FIG.6

LINEAR coRREcmR PATENTED 5 sum '09 or 17 I l i 27-iNTEGRATOR 1 FIG.IO

PATENTED 5 I974 sum r 09 or 17 INPUT MATRICES MULT FILTER FIG.13

REFERENCE RRREL 1 P R RETURN MATRlCES a K 1+2x1'p+I p 1 PROCESS 20 RRLR 19 102 1 LINEAR f FILTEIR T R LINEAR 18 CORRECTOR PATENTED SHEET REFERENCE :40am

FIGM- RETURN MATRICES 18\/MULT.

MuLT. 1 1 MULT.

PATENTED 51974 sum '13 or 17! FIG/i7 PATENTEDMAR 5l974 SHEET i l 0F 17 PATENTEDHAR 914 sum 15 or 17 FIGIQ PATENTEDNAR 51914 sum r16 UF17 PAIENTEDHAR 51914 SHEET I17 0F 1'? lllllilllillllllllllIllllllIllll ARRANGEMENT FOR CONTROLLING PROCESSES The present invention relates to control means for processes, in particular for processes involving a plural ity of control variables and an output variable or a plurality of measurable output variables depending in complex manner on the various control variables.

Such a process is encountered for example in distilling or fractionating columns at the inlet of which a flow rate and a temperature are controlled and at the outlet of which product concentration is measured in heat exchangers in which at the inlet flow rates and temperatures are controlled and at the outlet a temperature is measured, in alternators the absorbed active and reac tive energy of which is controlled and the supplied voltage and frequency of which are measured. This applies also to the piloting of a machine such as an aircraft.

In these processes, the parameters vary rapidly and the transfer matrices between input magnitudes and output magnitudes are unknown and are variable in time. Now, the control means utilized at the present day necessitate, if they are to be carried into effect, some knowledge of the relationships between input magnitudes and output magnitudes of the process.

According to the present invention, it has been found that it is possible to provide control means for monovariable or multivariable systems processing the input magnitudes or variables of the process in order that the output magnitudes or variables thereof may follow the output variables of a reference model, without it being necessary to know, a priori, the relationships existing between the input variables and the output variables. For this purpose, there is employed as main information, the deviation between the output .vectors of the model and of the process and, on the basis of this deviation, the synthesis of the control vector is formed.

More precisely, the process control means according to the invention is of the type which elaborates, starting from a reference model, a process control vector which is a function of the input vector of the model, of the output vector of the process and of the generalized deviation vector (the difference between the output vector of the model and that of the process) through intermediary of proportional-term matrices, called respectively the process input matrix, the process return matrix and the generalized deviation matrix, the firstor the last of the said matrices optionally being zero, and it is characterized in that it superposes on the process control vector defined hereinabove a supplementary control vector which is a function of the so-called determinate vectors constituted by the generalized deviation vector and at least one of two following vectors: the input vector of the model and the output vector of the process; and which is elaborated by a computer block comprising a linear portion processing the generalized deviation vector in such manner that the transfer matrix which would be established by the connection in series of the model and of the said linear portion is true and positive, and the nonlinear portion constituted by subassemblies each of which processes one of the components of the determinate vectors and each of which comprises, for each component of the output vector of the linear portion, a first multiplier the inputs of which receive the said component of the determinate vector and the said component of the vector of the output of the linear portion and the output of which controls, via a linear filter the transfer function of which is positive or zero at the positive true portion, a second multiplier the further input of which receives the same component of the determinate vector, the outputs of the various second multipliers of a subassembly being added together to yield the output of the said subassembly and the outputs of the various subassemblies of the nonlinear portion being added together in such a manner as to constitute the supplementary control vector.

The expression input vector is to be understood to mean the ordinate assembly of the variables of magnitudes at the input which constitute the components of the input vector, and the expression output vector" i is to be understood to mean the ordinate assembly of the variables of magnitudes at the output. A matrix is an operator which establishes linear combinations between the components of the vector (input vector), so as to-define a further vector (output vector), but, here, the term matrix is applied both to this mathematical operator and also to the means permitting the carrying into effect of the said combination and which will generally be constituted by an assembly of operational amplifiers interconnected in such manner as to satisfy the desired linear relationships.

Of course, the reference model determining the performances desired for the process must be selected in such manner as to be compatible with the process dynamics. In particular, it is necessary 'to take account, on selecting the reference model, of the maximum energy available for controlling the process, since the latter determines the maximum dynamic performances.

The values of the parameters of the linear and nonlinear portions of the computerblock are determined in such manner that the supplementary control vector undergoes rapid variations relative to the process dynamics. In differentiation from known adaptive systems, the variation velocity of the control system parameters is of the same order of magnitude as the process dynamics (the condition vectors and the parameters vary with analogous dynamics).

Further features of the invention will become appar ent from the description of examples of embodiment given hereinbelow in non-[imitative manner, with the aid of the accompanying diagrammatic drawings.

FIG. 1 shows the basic scheme of a known control means, and

FIG. 2 shows the modifications introduced by the invention into the said basic scheme;

FIG. 3 is a symbolic diagram utilized for determining the linear portion of the computer block or unit;

FIG. 4 .shows a subassembly of the nonlinear portion of the computer block;

FIG. 5 shows the association of the subassemblies of FIG. 4;

FIG. 6 is a general diagram of the control means, again showing the subassemblies of FIG. 4 and the association thereof in accordance with FIG. 5;

FIGS. 7, 8, 9, and 10 show examples of embodiment of the linear filters of the subassemblies of the nonlinear portion of the computer block or unit;

FIG. 11 shows the linear portion of the computer block;

FIG. 12 illustrates an example of application to a monovan'able process with a model of the first order;

FIG. 13 shows a first example of application to a process of the second order having a model of the first order;

FIG. 14 shows an example of application to a monovariable process having a model of the second order;

FIG. 15 shows an overall view of control means having linear filters at the output of the process and of the model;

FIG. 16 shows the elementary structure of a linear filter;

FIG. 17 shows the assembly of filters in respect of FIG. 16, with an addition device for forming the linear portion of the computer block;

FIG. 18 is a general diagram of the control means, showing the possibilities for utilization of data available on the linear filters;

FIG. 19 is a simplified diagram of the control means in the case of dynamic behavior differing only slightly from the process without control means and from the model;

FIG. 20 shows an example, differing from that of FIG. 14, of application to a monovariable process having a second order model; and

FIG. 21 shows the numerical version of FIG. 15, which is capable of being programmed on a process computer.

In the known diagram of FIG. 1, a process 1 is controlled to exhibit the same performances at those of a reference model 2. The process control vector E is processed on the basis of the input vector U of the model, of the process output vector 0,, and of the generalized deviation vector obtained in a comparator 3 receiving the vector 0,, and the vector 0,, of the model output. This processing of the vector E is effected by means of process input matrices 4, process-return matrices 5 and generalized deviation matrices 6 and also adder matrices 7 and 8.

The diagram of FIG. 2 contains the elements of FIG. 1, i.e., matrices 4, 5, and 6 the outputs of which are added in an adder 9. However, there has been introduced, according to the invention, a computer block or unit 10 processing a supplementary control vector 5 added, in an adder 11, to the control vector E according to FIG. 1.

The said computer block 10 consists of a linear portion constituted by a linear corrector 12 receiving the generalized deviation vector 6 and providing for hyperstability of the system, and of a nonlinear portion 13 receiving the output vector v of the linear corrector 12 the input vector U of the model, the output vector 0,, of the process and the generalized deviation vector 6, and supplying the supplementary control vector 5.

FIG. 3 is a symbolic diagram permitting determination of the linear corrector 12. If there were connected in series between an input 14 and an output 15, as shown in this figure, the transfer function M (p) model 2 and the transfer function Z (p) linear corrector 12, the transfer matrix 16 obtained between the input 14 and the output Z(p).M(p) would be true and positive. Thus, Z(p) is determined as a function of the model 2. Z(p) produces a plurality of successive derivations of the generalized deflection vector 6, and there will be given later an embodiment of the linear corrector 12 involving linear filters, whereby it becomes possible to eliminate the disadvantages due to the noise present on the output vector of the process.

posed of the following elements connected in series: a I

first multiplier 18, a linear filter 19 characterized by a transfer matrix having a true positive or zero portion, and a second multiplier 20. Each of these groups of elements receives the component arriving at 17 and one of the components 1 to v of the output vector v of the linear corrector 12. The outputs of the various groups are summated in summation means 21 to afford a partial component of the supplementary control vector 5: 5, (U), f, (6,,) or if, (6), depending on whether the subassembly is processing the vector U, the vector 0,, or the vector e.

FIG. 5 shows the association of subassemblies 22 such as that of FIG. 4 with summation means 23 each receiving a partial component (U), a partial component g, (6,) and a partial component g, e) and supplying one of the components 5,, to g of the supplementary control vector 5.

FIG. 6 is a general diagram of the control system according to that of FIG. 2, wherein there is shown the internal structure of the nonlinear portion 13 as apparent from FIGS. 4 and 5, employing the same reference numerals and the double lines designating a vector whereas the single lines designate a vector component.

FIGS. 7, 8, 9, and 10 show examples of embodiment of the linear filter 19. In the example of FIG. 7, the linear filter 19 consists of a transfer function element 24 K,,/1+T,, and a transfer function element 25 K, connected in parallel in such manner that the transfer function of the filter 19 is In the example of FIG. 8, the filter 19 consists of a single transfer function K element 26. In the case of FIG. 9, two elements 27 and 28 which are associated with transfer functions respectively K ,p and K i.e., an integrator and a gain, are connected in parallel and impart to the filter the transfer function K p-l-K ,p In the example shown in FIG. 10, the filter is a P.I.D. corrector having the transfer function K p K p+K /p FIG. 11 shows the diagram of a linear corrector 12 of a type which may be utilized in the case of FIG.- 6. The said corrector comprises, for a component 6, of the vector 5, an assembly of successive shunting devices connected in series, starting from the input 29 of the corrector; the said shunting devices have all been given the reference 30. Their number depends on the number n of successive shunts to be effected (in accordance with the expression of Z(p) calculated by the process mentioned with reference to FIG. 3). The output of each shunting means 30 is associated with means 31 of appropriate coefficient: a a,,,,, and the outputs of the means 31 are added in predetermined manner by the matrix Z(p) in summation means 32, to produce at 33 the output vector v of the corrector 12.

FIG. 12 shows an example of application to the control of a monovariable process the technological char- 

1. In an arrangement for controlling processes responsive to a plurality of control variables and controlled by a process control vector which is a function of the input vector of a model system, of the output vector of the control process system and of the generalized deviation vector formed by the difference between the output vector of the model system and that of the control process system, including a process input matrix having an input receiving said input vector, a first summing means receiving the output of said process input matrix for summing vector signals applied thereto, second summing means connected to the outputs of said model system and said control process system for summing the vector signals received, a process return matrix connected between the output of said control process system and an input of said first summing means, and a generalized deviation matrix connected between the output of said second summing means and an input of said first summing means, the improvement comprising supplementary control means connected to the outputs of said second summing means and said control process system and receiving said input vector for superimposing on the control signal applied to the input of said control process system from said first summing means a supplementary control vector which is a function of at least one of the generalized deviation vector, the model system input vector or the control process system output vector.
 2. The combination according to claim 1 wherein said supplementary control means includes a computer block comprising linear corrector means for processing the generalized deviation vector so as to stabilize the system and nonlinear means connected to said linear corrector means and including a plurality of subassemblies each processing one of the components of the determinant vectors, each subassembly comprising for each component of the output vector of the linear corrector means, a first multiplier receiving said vector signals, a linear filter connected to the output of said first multiplier a second multiplier connected to the output of said linear filter, and a first adder connected to the outputs of all of the second multipliers of the respective subassembly, further including a second adder connected to all of said first adders and providing said supplementary control vector to an input of said first summing means.
 3. The combination according to claim 2 characterized in that the values of the parameters of said linear corrector means and nonlinear means of the computer block adjust the supplementary control vector so that it undergoes rapid variations relative to the process dynamics.
 4. The combination according to claim 3 characterized in that the linear filters of the subassemblies of the nonlinear means of the computer block are constituted by transfer function operators having a positive or zero portion.
 5. The combination according to claim 4 characterized in that said linear corrector means of the computer block comprises a first linear filter processing the process output vector, a second linear filter processing the output vector of the model system, a comparator means connected between the outputs of the same order of the output vectors of the said filters and to said nonlinear means, and a balancing and addition device receiving the outputs of said comparator means and supplying the output vector of the said linear corrector means of the computer block.
 6. The combination according to claim 4 characterized in that said linear corrector means of the computer block comprises a linear filter connectEd to the output of said second summing means for processing the generalized deviation vector and a balancing and addition device connected to receive the successive outputs of the output vector of the last linear filter and supplying the output vector of the said linear corrector means of the computer block.
 7. The combination according to claim 5 characterized in that the nonlinear means of the computer block processes at least one of the determinant vectors after passage of the latter through a linear filter.
 8. The combination according to claim 5 characterized in that said nonlinear means of the computer block is connected to process also the successive shunt vectors of the output vector of the linear filter processing the process output vector, the successive shunt vectors of the generalized deviation filter vector measurable on the comparators, the successive shunt vectors of the output vector of the linear filter processing the input vector of the model.
 9. The combination according to claim 2 characterized in that said linear corrector means of the computer block comprises a first linear filter processing the process output vector, a second linear filter processing the output vector of the model system, a comparator means connected between the outputs of the same order of the output vectors of the said filters and to said nonlinear means, and a balancing and addition device receiving the outputs of said comparator means and supplying the output vector of the said linear corrector means of the computer block.
 10. The combination according to claim 2 characterized in that said linear corrector means of the computer block comprises a linear filter connected to the output of said second summing means for processing the generalized deviation vector and a balancing and addition device connected to receive the successive outputs of the output vector of the last linear filter and supplying the output vector of the said linear corrector means of the computer block. 